Selectively operable valves may be used in some circumstances to improve fuel economy, emissions, and performance of a piston driven internal combustion engine. Operation of individual valves may be based on a single or a combination of engine operating conditions so that the number of operating valves can be adjusted to meet demand and control objectives. Several different methods may be used to selectively operate or inhibit operation of valves including: mechanically inhibited cam actuated valves, electrically actuated valves, and electrohydraulic actuated valves. If valve degradation of selectively operated valves can be determined, it may be beneficial to control ignition spark during a combustion cycle of a cylinder based on the degradation.
One method to control engine ignition spark is described in U.S. Pat. No. 6,401,684. During an abnormal valve operating condition, at the transition from an open intake valve condition to a closed intake valve condition, this method attempts to delay ignition spark by increasing the duration of current flowing into the ignition coil until the second half of the power stroke in the respective cylinder. In addition, the method may attempt to inhibit ignition spark, if the ignition coil has not started to charge, when an abnormal valve condition is generated at the transition from a closed intake valve condition to an open intake valve condition. Furthermore, the method may also attempt to inhibit spark if an abnormal condition is generated at a transition from an open exhaust valve condition to a closed exhaust valve condition.
The inventors herein have recognized that the before-mentioned approach can have several disadvantages. For example, extending coil charging into the second half of the power stroke may produce more than a desirable amount of coil current which could degrade the ignition coil. Further, the method attempts to extend a spark event to a point that is late in the cylinder cycle. As a result, combustion may still occur since both spark and fuel can be present in the cylinder. If an intake valve remains open during combustion, the intake manifold temperature and pressure may increase more than desired. On the other hand, if an exhaust valve remains open during combustion, the exhaust valve temperature may increase more than desired. As such, following the approach taught in the prior art may lead to several issues.